In the current Long Term Evolution (LTE) system, only one carrier, with the maximal bandwidth of 20 Mhz, is allowed in a cell, as shown in FIG. 1A.
For an LTE-Advanced (LTE-A) system, its peak rate has been greatly improved compared with that of the LTE system, and a downlink peak rate of 1 Gbps and an uplink peak rate of 500 Mbps are required in the LTE-A system. Apparently, a bandwidth of 20 Mhz fails to meet such a requirement. Carrier Aggregation (CA) technology is introduced for the purpose that the LTE-A system is capable of meeting the requirement, namely, a plurality of continuous or discontinuous carriers are aggregated together in the same cell, and when needed, serve the user equipment (UE) simultaneously to provide desired rates, therefore, the LTE-A system is a multi-carrier system. To ensure that the UE of the LTE-A system is capable of operating in each aggregated carrier, each carrier has a bandwidth of not more than 20 Mhz. The CA technology for the LTE-A system is shown in FIG. 1B.
In the LTE-A system in FIG. 1B, 4 carriers are aggregated. A base station may carry out data transmission on the 4 carriers simultaneously with the UE, to improve system throughput.
For a Frequency Division Duplex (FDD) system, a User Equipment (UE) receives downlink data in a sub-frame n−4, and feeds back, in an uplink sub-frame a signaling whether data in the downlink sub-frame needs to be retransmitted (i.e., Acknowledgement/Non-acknowledgement (ACK/NACK)). Upon carrier aggregation, ACK/NACK information corresponding to a plurality of downlink carriers in the sub-frame n−4 is fed back in the uplink sub-frame n simultaneously.
For a Time Division Duplex (TDD) system, UE may feed back ACK/NACK information corresponding to a plurality of downlink sub-frames in one uplink sub-frame, i.e., after demodulating and decoding data in the downlink sub-frame n−k, the UE feeds back, on the uplink sub-frame n, to the base station signaling (i.e. ACK/NACK) whether the data in the downlink sub-frame needs to be retransmitted, where k∈K, and the value of the set K is related to uplink/downlink configurations of the system and specific sub-frame serial numbers, specially shown in Table 1.
TABLE 1Provision on Uplink Feedback for Downlink TransmissionUplink andDownlinkConfigurationSub-Frame Serial NumbersStructures01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 6, 4————8, 7, 6, 4——3——11, 7, 66, 55, 4—————4——12, 11, 8, 77, 6, 5, 4——————5——13, 12, 11, 9, 8,———————7, 6, 5, 46——775——77—
A plurality of radio frames are sequentially arranged, i.e., if the last sub-frame in the radio frame a is sub-frame k, then the first sub-frame in the radio frame a+1 is sub-frame k+1. Only the example of one radio frame is given in Table 1 to show the conditions of K corresponding to each uplink sub-frame, wherein if n−k<0, then this represents the downlink sub-frame in the previous radio frame.
In the LTE system, the UE needs to feed Channel State Information (CSI) back to the base station. The base station performs downlink dynamic scheduling by using the CSI fed back by the UE.
Based on different trigger mechanisms, CSI is classified into two types: periodic CSI and non-periodic CSI. The reporting period of the periodic CSI and the shift in the period are semi-statically configured by the base station via Radio Resource Control (RRC) signaling, and the UE transmits the CSI in a particular uplink sub-frame according to configuration information. In a sub-frame without uplink data transmission, the periodic CSI is transmitted by using a Physical Uplink Control Channel (PUCCH), and the PUCCH resource for transmitting the periodic CSI is semi-statically configured by the base station.
In an LTE-A Release-10 (Rel-10) carrier aggregation system, the parameters of the periodic CSI of different component carriers are configured independently, the UE only feeds back the periodic CSI of one component carrier in each reporting sub-frame, and if there are collisions of the periodic CSI of a plurality of component carriers, the periodic CSI with the highest priority is fed back in accordance with the predetermined priorities.
The non-periodic CSI is triggered by the base station via downlink scheduling signaling, the UE reports CSI only after receiving trigger signaling, and the non-periodic CSI is transmitted by using a Physical Uplink Shared Channel (PUSCH). UE may report the non-periodic CSI of a plurality of component carriers simultaneously in accordance with the trigger condition of the base station.
In an LTE-A Rel-11 system, simultaneous feedback of multi-carrier ACK/NACK information and periodic CSI will be supported in order to improve the downlink transmission efficiency of the system and reduce the loss probability of the periodic CSI, however, the scheme for simultaneous feedback of multi-carrier ACK/NACK and periodic CSI has not been found yet at present.